Stable platforms



Aug. 15, 1967 s. M. ELLIS STABLE PLATFORMS 5 Sheets-Sheet 1 Filed Sept. 14, 1964 BY M, M

ATTORA/EX;

S. M. ELLIS STABLE PLATFORMS Aug. 15, 1967 ,5 Sheets-Sheet 2 Filed Sept. 14, 1964 lN'l/E/VTOR S74FFOE0 All-4L Cal/1151145 A TTOIZNEYS Aug. 15, 1967 s. M. ELLIS 3,335,614

STABLE PLATFORMS Filed Sept. 14, 1964 3 Sheets-Sheet 5 INVEN 70/2 SM/TOEO Mira/vans WM, M25! M A rTok/vEKS United States Patent "ice 3,335,614 STABLE PLATFORMS Stafford Malcolm Ellis, St. Albans, England, assignor to Elliott Brothers (London) Limited, Lewisham, London, England, a British company Filed Sept. 14, 1964, Ser. No. 396,097 Claims priority, application Great Britain, June 15, 1961, 21,749/61; July 9, 1964, 28,461/64 26 Claims. (Cl. 74-5.34)

This invention relates to stable platforms. This application is a continuation-in-part of my copending application Ser. No. 202,456, filed on June 14, 1962, and entitled, Stable Platforms, which application is now abandoned.

Known stable platforms are usually of three-axis or four-axis type, the former being used where limited angular freedom sufi'ices, and the latter being used where full angular freedom is required. These three-axis and four-axis type stable platforms have hitherto included a stable element, on which gyroscopes and other sensing units are mounted, the elements being supported centrally within two and three gimbal rings respectively, the mounting of the element being such that it is capable of remaining angularly stationary with respect to space, regardless of the angular movement applied in roll, pitch and azimuth to the structure, on which the stable platform is mounted.

One disadvantage of these known platforms is that they are heavy because gimbal rings have a high weight stiffness ratio due to their shape. Another disadvantage is that when angular movements are applied to the supporting structure about more than one axis simultaneously the outer gimbal ring has to be accelerated in space to save the stable element from being disturbed. A further disadvantage is that accessibility of the stable element is restricted by the gimbal rings.

An object of the present invention is to provide new or improved stable platforms by which the above-mentioned disadvantages are avoided.

A stable platform according to the invention comprises a plurality of stable elements rotatable about individual azimuth axes and mounted in a plane normal to these axes substantially symmetrically around a centre on a frame supported from said centre by mechanism which establishes the desired roll and pitch freedom of said frame and is itself carried by an arm of a supporting structure which lies approximately in said plane when the frame is in its mid position.

In my above-mentioned application it is proposed that there should be at least three stable elements mounted other than in a straight line and coupled together preferably by a link connected to arms of equal length, each mounted on and at right angles to the spindle of an element and pivoted at its other end to the link, all of said arms being oriented identically to one another in any position of the link.

The frame may be one having a substantially C, U, V, horseshoe or other suitable shape to provide an opening for the entry of the supporting arm.

In stable platforms according to the invention the stable elements are conveniently mounted on an open-side frame of suitable shape in plan (for instance, of C, U or horseshoe shape as already intimated), for rotation about separate azimuth axes on spindles journalled in said frame, said stable elements being equiangularly arranged relatively one to another and equidistant radially from the centre of symmetry of the frame.

From and at right angles to corresponding ends of the spindles of the stable elements extend arms for pivotal connection with a link lying parallel to the frame, and conveniently having the same general shape as the frame,

3,335,614 Patented Aug. 15, 1967 the connecting arms being of equal length and arranged so as to be identically radially directed at all times.

Through the opening in the side of the frame a bearing extends inwardly in cantilever manner from a supporting bracket or other structure, a first shaft being journalled in said bearing and constituting a roll axis for the platform. In the case of a three-axis arrangement this first shaft forms the single roll axis and is joined to the centre of a second shaft at right angles which is journalled by its opposite ends in the frame and forms the pitch axis. In the case of one four-axis arrangement the said first shaft journalled in the inwardly directed bearing forms the outer roll axis and has a transverse head carrying the second shaft, or its equivalent, viz., axially aligned trunnions, forming the pitch axis, said second shaft not extending to join the frame. The inner roll axis in this four-axis arrangement is constituted by a third shaft which, when in its mid-position, is coaxial with said first shaft, said third shaft being pivotally connected to the above-mentioned second shaft of the transverse head of the first shaft.

In another four-axis arrangement, the second shaft is vertically disposed, when in its mid-position, and is journalled in a gimbal ring from which extend diametrically aligned axles which have their outer ends journalled in the frame and together constitute the third shaft, which, in its mid-position, lies in the same plane but at right angles to the first shaft.

It has now been found that for certain arrangements a stable platform may comprise only two stable elements, on one of which a two-degree-of-freedom gyroscope is mounted; the other stable element may support either a one-degree-of-freedom gyroscope or a two-degree-of-freedom gyroscope.

Two-degree-of-freedom gyroscopes are known per se, and in one such device suitable for the present purpose the rotor is supported centrally on a substantially spherical bearing with a volume of gas between two parts of the bearing. The rotor is thus able to tilt about two axes which are mutually perpendicular. Suitable pick-off means are provided in the usual way to detect such tilt and provide signals which can be used for servo and stabilising purposes. With two stable elements mounted on the frame, two axes are stabilised by one gyroscope and the other axis is stabilised by the other gyroscope. If the second gyroscope is also of the two-degree-of-freedom type its second axis may be used for monitoring purposes.

Instead of the elements being linked mechanically for maintaining their orientation, they may be linked electrically by electric motors and control circuits, and this arrangement is preferable in some applications.

In some gyroscopes inaccuracies of operation may occur due to manufacturing inaccuracies, but these can largely be eliminated by continuous rotation of the casing containing the gyroscope at an appropriate speed. It is therefore preferred to provide means for rotating the casing of the vertical gyroscope, and in certain cases the casing of the azimuth gyroscope may also be rotated.

The invention is illustrated, by way of example, in the accompanying diagrammatic drawings, wherein:

FIGURE 1 illustrates a three-axis platform,

FIGURES 2 and 3 illustrate four-axis platforms,

FIGURES 4 and 5 illustrate maintained orientation of the connecting arms of four stable elements, with a common C-shaped link, as employed in each of the arrangements illustrated in FIGURES 1, 2 and 3,

FIGURES 6 and 7 are respectively a simple diagram and a fragmentary perspective view of a four-axis platform employing two stable elements, at least one of which comprises a two-degree-of-freedom gyroscope, and

FIGURE 8 is an electrical diagram illustrating the principle of electrically coupling together a plurality of stable elements.

In FIGURES 1 to. of the drawings the same or equivalent parts bear the same reference numbers.

In the embodiment illustrated in FIGURE 1, the single roll axis for the platform is constituted by a first shaft 1 journalled in a cantiliver bearing 2 extending from a supporting bracket 3 into a C-shaped frame 4 through the mouth of the C. Shaft 1 is secured at right angles to a second shaft 5, which forms the pitch axis of the platform and extends transversely across frame 4, its outer ends being journalled in said frame. The frame 4 is conveniently of channel shape in cross section, with the channel mouth opening outwardly, so that four stable elements 6 may be accommodated partly within the frame channel. The stable elements have their azimuth axes equiangularly and concentrically disposed about a centre of symmetry, which lies at the intersection between shafts 1 and 5. Above and parallel to frame 4, and also of C-shape, is a link 7 to which are pivotally connected the outer ends of equal-length arms 8 extending from spindles 9 which support the stable elements 6 on frame 4.

The four-axis arrangement shown in FIGURE 2 employs the same kind of frame 4, stable element 6, link 7 and arms 8 as in FIGURE 1, but here the shaft 10, supported as in FIGURE 1 by hearing 2 and bracket 3, forms the outer roll axis of the platform, the inner roll axis being constituted by a third shaft 11 arranged, when in mid-position, coaxial with shaft and pivotally con-' nected thereto through a forked head 12 embracing a short pitch axis axle 13, which in this case does not extend to join with frame 4.

Another four-axis arrangement is illustrated in FIG- URE 3, in which a single roll axis shaft 10 (in this case shown supported by bearing 2 from a binnacle frame 15) is pivotally connected to a gimbal ring 16 through a short cross axle 17, which comes into use as supplementary roll freedom is and when the vehicle in which the platform is mounted is pointed approximately vertically upward or downward. The gimbal ring 16 has diametrical extensions 18 which are journalled in frame 4 and together form the pitch axis of the platform.

FIGURES 4 and 5 show how the link maintains orientation of the equal length arms 8.

The bearing 2 and the various arrangements of shafts between bearing 2 and frame 4 constitute what is herein before referred to generally as the mechanism which establishes roll and pitch freedom.

The variety of ways in which this mechanism can be arranged indicate the advantages to be gained by the use according to the present invention to what may be termed inside-out constructions, that is, three or more stable elements arranged around the outside of a frame with pitch and roll freedom.

Considering now the four-axis stable platform illustrated in FIGURES 6 and 7, a shaft 21 journalled in a cantilever bearing 22 forms the inner roll axis of the platform and a shaft 23 journalled in a bearing 24 forms the outer roll axis. The shaft 21 is arranged, when in mid-position, to be coaxial with shaft 23 and pivotally connected thereto through a forked head 25 embracing a short pitch axis spindle 26. The bearing 22 is connected to the central point of a C-shaped frame 27. At one end of the frame is mounted a first stable element 28, comprising an azimuth gyroscope with sensing elements, and a second stable element 29, comprising a vertical gyroscope with sensing elements. The casing of the element 29 is arranged to be rotated about its vertical axis continuously at an appropriate speed to eliminate errors due to manufacturing inaccuracies. The stable element 29 comprises a two-degree-of-freedom gyroscope, and preferably the element 28 does also.

Three accelerometers are provided to stabilise the system with respect to space. Two accelerometers 30 are shown mounted on the stable element 28, and the third accelerometer (not shown) for vertical movement is mounted on the pitch frame 27, which is already stabilised with respect to the horizontal. It will be appreciated that all three accelerometers could alternatively be mounted on one of the stable elements.

The two stable elements may be coupled together by a mechanical linkage as in the preceding examples, but preferably they are coupled electrically, in order to maintain them in orientation, by the system illustrated in FIGURE 8. As shown in FIGURE 8, the stable element 28, mounted in a gimbal 31, is drivingly coupled to a synchro transmitter 32 by gearing 33. The angular orientation of the element 28 with respect to the gimbal 31 is thus transmitted to a synchro control transformer 34, which forms part of a servo mechanism including a high gain electronic amplifier 35 and a motor/ tachometer combination 36. The output shaft 37 of the synchro control transformer 34 repeats this angular orientation PH, which is applied to one input of a summing differential gearbox 38. The other input 39 of the differential gearbox 38 is coupled to a constant speed motor 40, which rotates at a constant rate PZ-PH, where P2 is the required orientation of the element 29 with respect to the gimbal 31. The output shaft 41 of the differential gearbox therefore rotates at a rate P2, and this output is applied to a further synchro transmitter 42. A synchro control transformer 43, which is controlled by the signal from the transmitter 42, is coupled to the stable element 29 by gearing 44 and by servo means including a high gain electronic amplifier 45 and a motor/ tachometer combination 46. The element 29 is thus controlled so as to rotate with constant angular velocity with respect to the element 28, irrespective of any movement of the latter with respect to the gimbal.

If desired the element 29 may be coupled directly to the element 28, the synchro control transformer 43 being driven from the synchro transmitter 32.

It will be evident to those acquainted with the art that a stable platform in accordance with this invention necessarily requires for its operation many conventional parts which, for clearness, are not shown in the drawings. For instance, in accordance with standard practice, servometers would be coupled to the roll, pitch and azimuth shafts and controlled by electrical signals [from gyroscopes mounted on the stable elements.

I claim:

1. A stable platform comprising a plurality of stable elements rotatable about individual azimuth axes and mounted in a plane normal to these axes, substantially symmetrically around a centre, on a frame supported from said centre by mechanism which establishes the desired roll and pitch freedom of said frame and is itself carried by an arm of a supporting structure which lies approximately in said plane when the frame is in it mid-position.

2. A stable platform comprising an open-side pivotal frame lying substantially horizontal when in mid-position, a mechanism for supporting said frame and for establishing roll and pitch freedom thereof, means for supporting said mechanism from the centre of symmetry of said frame through the side opening thereof, and a plurality of stable elements mounted on said frame for rotation about individual azimuth axes and disposed concentrically around said centre of symmetry of the frame.

3. A stable platform as claimed in claim 1, wherein said mechanism comprises means for supporting said frame for pivotal movement about roll and pitch axes, and means for coupling together said stable elements to maintain them in orientation.

4. A stable platform comprising a supporting structure having a horizontal arm, a pivotal frame having a side opening and lying when in mid-position in a horizontal plane, with said a-rm extending inwards through said opening toward the centre of symmetry of said frame, mechanism interposed between said arm and said frame for supporting the latter with freedom to move about pitch and roll axes, a plurality of stable elements mounted y v on said frame concentrically around the centre of symmetry thereof and about individual azimuth axes lying normal to the plane of the frame, and means interconnecting said stable elements for maintenance of their orientation.

5. A stable platform comprising a plurality of stable elements rotatable about individual azimuth axes, a frame carrying said stable elements with their azimuth axes in planes normal to the plane in which the frame is lying and substantially symmetrically around the centre of symmetry of said frame, mechanism for supporting said frame from its said centre of symmetry to establish desired roll and pitch freedom of said frame, and a supporting structure having an arm for carrying said frame supporting mechanism and lying approximately in a horizontal plane when the frame is in its mid-position.

6. A stable platform as claimed in claim 5, characterised in that the frame has a side opening for the entry of said supporting arm.

7. A stable platform as claimed in claim 5, including means whereby said symmetrically disposed stable elements are coupled together to maintain orientation thereof.

8. A stable platform as claimed in claim 7, wherein said stable element coupling means comprises a link and arms of equal length pivotally connected to said link and each mounted on said frame by a spindle disposed at right angles to the plane of the frame.

9. A stable platform as claimed in claim 8, in which said coupling link has a shape approximately the same as that of the frame.

10. A stable platform as claimed in claim 5, characterised in that said frame is of channel form in cross section with the mouth of the channel opening outwardly and that the stable elements are pivotally mounted at least partially within said frame channel.

11. A stable platform as claimed in claim 5, wherein said mechanism includes a first shaft forming a single roll axis, for the platform and a second shaft joined at its centre at right angles to said first shaft, said" second shaft being journalled by its opposite ends in said frame and forming the pitch axis of the platform.

12. A stable platform as claimed in claim 5, wherein said mechanism includes a first shaft forming an outer roll axis for the platform, a cross shaft joined to said first shaft and lying in the same plane as said first shaft to form a pitch axis for the platform, and a third shaft coaxial with said first shaft to form an inner roll axis for the platform, said third shaft being connected to said frame and extending therefrom toward said first shaft and said third shaft having a forked head for embracing said cross shaft endways.

13. A stable platform as claimed in claim 5, wherein said mechanism includes a first shaft forming a single roll axis for the platform, a cross shaft joined to said first shaft and lying in a plane at right angles thereto, a gimbal ring encircling and journalled to said cross shaft and having diametrical extensions journalled in said frame and forming a pitch axis therefor.

14. A stable platform comprising a supporting structure having a bearing arm; a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said bearing arm to extend therethrough toward the centre of symmetry of said frame; a roll axis shaft journalled in said bearing arm, with its inner end extending to the centre of symmetry of said frame; a pitch axis shaft fixed midway of its length to said roll axis shaft and at said centre of symmetry and having its opposite ends journalled in said frame, and a plurality of stable elements having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said interconnected roll axis and pitch axis shafts.

15. A stable platform as claimed in claim 14, characterized in that said stable element spindles all carry equal length arms radiating from said spindles at right angles,

said arms being pivotally connected to a common link to maintain said stable elements in orientation.

16. A stable element as claimed in claim 15, wherein said link lies parallel to said frame and both the frame and the link are C-shaped.

17. A stable platform comprising a supporting structure having a bearing arm, a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said heating arm to extend therethrough toward the centre of symmetry of said frame; an outer roll axis shaft journalled in said bearing arm, with its inner end extending to the centre of symmetry of said frame; a pitch axis axle fixed to said outer roll axis shaft end at said centre of symmetry; said pitch axis axle lying in the same plane as said outer roll axis shaft; an inner roll axis shaft coaxial with said outer roll axis shaft, journalled at one end in said frame and having a forked head at its other end for pivotally supporting and embracing said pitch axis axle endways and a plurality of stable elements having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said interconnected outer and inner roll axis and pitch axis shafts.

18. A stable platform comprising a supporting structure having a bearing arm; a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said bearing arm to extend therethrough toward the centre of symmetry of said frame; a roll axis shaft journalled in said bearing arm, with its inner end extending to the centre of symmetry of said frame; a cross axle fitted to said roll axis shaft end at said centre of symmetry, said cross axle lying in a plane at right angles to that of said roll axis shaft; a gimbal ring encircling said cross axle and journalled on the ends thereof for pivotal movement, said gimbal ring having diametrical extensions lying in the same plane as the roll axis shaft and extending out to and journalled in said frame to constitute pitch axis shaft means for the platform, and a plurality of stable elements having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said roll axis and pitch axis shafts.

19. A stable platform comprising a supporting structure having a bearing arm; a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said bearing arm to extend therethrough toward the centre of symmetry of said frame; an outer roll axis shaft journalled in said bearing arm, with its inner and extending to the centre of symmetry of said frame; a pitch axis axle fixed to said outer roll axis shaft end at said centre of symmetry; said pitch axis axle lying in the same plane as said outer roll axis shaft; an inner roll axis shaft coaxial with said outer roll axis shaft, journalled at one end in said frame and having a forked head at its other end for pivotally supporting and embracing said pitch axis axle endways and at least three stable elements having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said interconnected outer and inner roll axis and pitch axis shafts.

20. A stable platform comprising a supporting structure having a bearingarm; a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said bearing arm to extend therethrough toward the centre of symmetry of said frame; a roll axis shaft journalled in said bearing arm, with its inner end extending to the centre of symmetry of said frame; a cross axle fixed to said roll axis shaft end at said centre of symmetry, said cross axle lying in a plane at right angles to that of said roll axis shaft; a gimbal ring encircling said cross axle and journalled on the ends thereof for pivotal movement, said gimbal ring having diametrical extensions lying in the same plane as the roll axis shaft and extending out to 7 I. and journalled in said frame to constitute pitch axis shaft means for the platform, and at least three stable elements having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said roll axis and pitch axis shafts.

21. A stable platform comprising a supporting structure having a horizontal arm, a pivotal frame having a side opening and lying when in mid-position in a horizontal plane with said arm extending inwards through said opening towards the centre of symmetry of said frame, mechanism interposed between said arm and said frame for supporting the latter with freedom to move about pitch and roll axes, first and second stable elements mounted on said frame symmetrically about the centre of symmetry thereof and about individual azimuth axes lying normal to the plane of the frame, at least one said stable element including a two-degree-of-freedom gyroscope, and electrical means coupling said stable elements for maintenance of their orientation.

22. A stable platform comprising a pair of stable elements rotatable about individual azimuth axes, at least one said stable element including a tWo-degree-of-freedom gyroscope having a rotatable casing, a frame for supporting said stable elements symmetrically about a common centre, means for supporting said frame for pivotal movement about roll and pitch axes, electrical means for coupling together said stable elements to maintain them in orientation, and means for continuously rotating the casing of said two-degree-of-freedom gyroscope.

23. A stable platform comprising a supporting structure having a bearing arm; a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said bearing arm to extend therethrough towards the centre of symmetry of said frame; an outer roll axis shaft journalled in said bearing arm with its inner end extending to the centre of symmetry of said frame; a pitch axis axle fixed to said outer roll axis shaft end at said centre of symmetry; said pitch axis axle lying in the same plane as said outer roll axis shaft; an inner roll axis shaft coaxial with said outer roll axis shaft, journalled at one end in said frame and having a forked head at its other end for pivotally supporting and embracing said pitch axis axle endways, and a pair of stable elements at least one of which includes a two-degree-of-freedom gyroscope, said stable elements having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said interconnected outer and inner roll axis and pitch axis shafts.

24. A stable platform comprising a supporting structure having a bearing arm; a symmetrically shaped frame having an opening in its side along the axis of symmetry of said frame, said side opening enabling said bearing arm to extend therethrough towards the centre of symmetry of said frame; a roll axis shaft journalled in said bearing arm with its inner end extending to the centre of symmetry of said frame; a cross axle fixed to said roll axis shaft end at said centre of symmetry, said cross axle lying in a plane at right angles to that of said roll axis shaft; a gimbal ring encircling said cross axle and journalled on the ends thereof for pivotal movement, said gimbal ring having diametrical extension lying in the same plane as the roll axis shaft and extending out to and journalled in said frame to constitute pitch axis shaft means for the platform, and first and second stable elements, at least one of which includes a tWo-degree-offreedom gyroscope, having spindles journalled in said frame to dispose individual azimuth axes of said stable elements normal to the plane of said roll axis and pitch axis shafts.

25. A multi-axis stable platform comprising a supporting structure having a horiozntal arm, a pivotal frame having a side opening and lying when in mid-position in a horizontal plane with said arm extending inwards through said side opening towards the centre of symmetry of said frame, mechanism interposed between said arm and said frame for supporting the latter with freedom to move about pitch and roll axes, a plurality of stable ele ments mounted on said frame symmetrically about the centre of symmetry thereof and about individual azimuth axes lying normal to the plane of the frame, at least one of said stable elements including a two-degree-offreedom gyroscope providing in respect of each of two axes of said platform one degree of freedom, and having a rotatable casing, electrical coupling means coupling said stable elements to maintain them in orientation, and means for continuously rotating said rotatable casing.

26. A stable platform as claimed in claim 3, which comprises at least three said stable elements.

References Cited UNITED STATES PATENTS 2,432,430 12/1947 Luboshez 745.37 2,811,785 11/1957 Braddon et al. 74-5.34 X 2,963,242 12/1960 Mueller 74-5.34 X 2,970,382 2/1961 Notomi 74-5.34 X

FRED C. MATTERN, JR., Primary Examiner.

I. D. PUFFER, C. I. HUSAR, Assistant Examiners. 

1. A STABLE PLATFORM COMPRISING A PLURALITY OF STABLE ELEMENTS ROTATABLE ABOUT INDIVIDUAL AZIMUTH AXES AND MOUNTED IN A PLANE NORMAL TO THESE AXES, SUBSTANTIALLY SYMMETRICALLY AROUND A CENTRE, ON A FRAME SUPPORTED FROM SAID CENTRE BY MECHANISM WHICH ESTABLISHES THE DESIRED ROLL AND PITCH FREEDOM OF SAID FRAME AND IS ITSELF CARRIED BY AN ARM OF A SUPPORTING STRUCTURE WHICH LIES APPROXIMATELY IN SAID PLANE WHEN THE FRAME IS IN IT MID-POSITION. 